A large number of commercial and factory or plant roofs are of a flat roof design wherein the roofing material itself is often of a built-up asphalt and, in more modern systems, of a single ply EPDM elastomeric sheet or membrane. In terms of securing a single ply EPDM membrane to the roof itself, one design utilizes a mechanical ballast system that uses a layer of stone over the membrane. While the ballast system is least expensive, it has the disadvantage of being quite heavy (approximately 10 pounds per sq. foot) thus requiring a heavy roof support structure and, in addition, the roof slope cannot exceed 10.degree..
Adhered roof membrane retention systems suffer from a cost penalty while mechanical fastening systems generally require a fixation to the roofing substrate via mechanical fasteners. There are two basic kinds of such mechanical fasteners, namely membrane penetrating and non-penetrating ones. Each of these types of fasteners has a number of favorable features and each of them is also subject to various drawbacks and disadvantages.
An example of a non-penetrating type fastener is shown in German Patent publication No. 2,433,669 to Ott, which discloses a membrane fastener comprising a lower disc attached to a roofing substrate by anchoring member. The roofing membrane is fitted over the lower disc and an upper disc is snapped over the lower disc to perfect the fastening and exert a sealing effect. A plug is then driven into the upper disc to expand the body thereof into an annular space provided in the lower disc to anchor the upper disc to the lower disc. Non-penetrating fastener or anchoring systems have the disadvantage of introducing wrinkles into the elastomeric membrane. Wrinkles are indicative of tension and tension, in rubber, is known to cause undesirable cracks.
Mechanical fastening systems, of the penetrating type, generally require fixation to the roofing substrate by a metal fastener with metal or rubberized nailing strips. U.S. Pat. No. 4,445,306 to Schauffele sets forth a mechanically attached roofing system wherein an elongated fastening bar is placed above the membrane and fastened to the roofing structure with fasteners such as screws or nails which are driven through the bar from the top thereof through the underlying membrane into the roofing structure. An elongated waterproof strip, sandwiched beneath the bottom of the bar and the membrane, and through which the fasteners pass, has its marginal sections wrapped upwardly around the bar to overlap each other above the bar and the head of each fastener.
U.S. Pat. No. 4,074,501 to Sandqvist discloses a method and apparatus for securing a sealing layer on a flat roof by means of a number of plates and screws passing through those plates. A membrane layer is attached to a roofing substrate by means of a plate composed of a semi-rigid material in which is formed a centrally located aperture into which is inserted a self-cutting screw that anchors the assembly to the roofing substrate. A bonding agent is required at the screw and the plate edges.
U.S. Pat. Nos. 4,455,804 and 4,467,581 to Francovitch both pertain to membrane anchors wherein the former utilizes a disc of rubber-like material having a central opening and downwardly inclined upper and lower surfaces, the lower surface having grooves for receiving mastic. A linear fastener extends through a central opening. The latter pertains to a resilient metal anchoring system composed of resilient metal that secures a roofing membrane to a substrate wherein the disc-like anchor, having downwardly facing cavities, is anchored to the substrate by a fastener. Grooves below the central region serve to seal the membrane around a perforation formed by the fastener and flexure zones on the outer periphery of the anchor further serve to seal the membrane.